Summary report: Pronghorn antelope abundance survey in south-central Washington February 25-26, 2015

By the start of the 20th century, pronghorn antelope had become extirpated from Washington. Ninety-nine pronghorns were reintroduced onto the Yakama Reservation, Washington in 2011 and many have since dispersed from their release locations. We conducted aerial surveys on February 25-26, 2015 in Benton, Klickitat, and Yakima Counties in south-central Washington, both on the Yakama Reservation and off the Reservation. The objective of the survey was to obtain a minimum population estimate for pronghorn. We counted a total of 106 pronghorns during our aerial survey and an additional 26 from ground surveys, for a total minimum population estimate of 132 pronghorns. The true abundance is likely to be underestimated because small group sizes (resulting from the early spring) made detecting animals difficult, and because we did not survey all areas where pronghorns have historically been observed. Additionally, coyotes might be at sufficiently high densities to keep pronghorn fawn survival low for this population. Human-induced mortality must be kept low to protect this small population for a few years.